The objectives are to continue the purification, isolation and characterization of human melanoma associated antigens (MAA), to study their specificity, and the mechanisms of their release by viable tumor cells. If successfully purified, MAA will be used to develop improved assays of humoral immunity to, and circulating antigens associated with, melanoma. The approach will be to radiolabel macromolecules on the surface of melanoma cells by the lactoperoxidase technique and cytoplasmic proteins with labelled amino acids. Macromolecules will be solubilized by lysis in nonionic detergents, or if "shed", collected in soluble form from culture media. MAA will be identified by double antibody antigen binding assay and radioimmunoassay, utilizing xenogeneic anti-melanoma antibodies exhaustively absorbed with normal tissues. Conventional biochemical procedures and solid phase immunoadsorbents will be used to purify MAA. Specificity will be studied by quantitative absorption, radioimmunoassay and comparison with labelled macromolecules on control cells. If successfully purified, several aspects of MAA biology relevant to understanding or modifying tumor growth will be studied, including: a) the immunogenicity of MAA in vivo, and methods of enhancing it, b) the mechanisms of release of MAA by viable cells, c) the effect of MAA release on the susceptibility of tumor cells to immune destruction, d) the utilization of purified MAA for the development of improved assays of antibodies to, and circulating antigens associated with, melanoma. If successful, these studies may provide tumor antigens useful for the specific immunotherapy of melanoma and for assays of the extent, prognosis and response to therapy of this cancer. Furthermore, we hope to understand, and thus influence, antigen release by tumor cells, a process which may have a profound impact on immune resistance to cancer.